'pus' originates from Latin, specifically the word 'pus' (genitive 'puris'), where 'pus' meant 'pus, matter from infection'.

'pus' changed from the Latin word 'pus' (attested in Classical and Medieval Latin) and passed into Middle English/early modern usage as 'pus', eventually becoming the modern English word 'pus'.

Initially, it meant 'pus; matter from infection', and over time this core meaning has largely remained unchanged in modern English.